The present invention relates to signal apparatus and more particularly to signal apparatus for causing oscillation of a signal beam through one or more selectable arcs and for selectively causing revolutions of the beam.
Without limiting the scope of intended applications of the inventive apparatus, the background of the invention is described in connection with the field of emergency vehicle warning lights. Prior signal beam apparatus of this type has had several light sources, e.g. one to provide a beam of light sweeping through a full circle, another light source to provide a beam of light oscillating through an arc forward of the vehicle, and still another source to provide a beam of light oscillating through an arc to the rear of the vehicle.
In emergency vehicle applications it is desirable to control the flash rate of the signal light apparatus according to conventional specifications when these apply. "Flash rate" is the number of flashes of light seen by a fixed observer per unit of time when the observer is within the arc traversed by the beam of light, but not at the extreme end of the arc.
The apparent intensity of a flash to an observer increases when the amount of electrical energy for an electric light source is increased but decreases as the angular velocity of the beam is increased. In general, the average angular velocity has to be increased if flash rate is to be increased. Often, however, the apparent intensity of the flashes is to be maintained above a specified level for a given flash rate. Also, prior art devices vary in their angular velocity through an arc of rotation. Accordingly, the amount of electrical energy used for the light source must be sufficient in such circumstances to set the apparent intensity above the specified level in the part of the arc in which the angular velocity is greatest. However, the electrical energy is then partly wasted during traversal of the rest of the arc. Furthermore, it is sometimes desirable to maintain a selected flash rate regardless of whether oscillation through an arc or continuous rotation through many full revolutions is selected by an operator of the vehicle.
U.S. Pat. No. 3,408,624 shows a signal device for emergency vehicles, which has lamps that are respectively mechanically oscillated to front, side, and rear.
U.S. Pat. No. 4,281,311 shows a rotating signal light which is continuously driven at a non-uniform speed of rotation for the purpose of enhancing light intensity in certain predetermined directions and reducing light intensity in other directions. Such warning lights are said therein to be conventionally rotated at a constant speed. A rotating lamp and motor are operated in a circle utilizing brushes riding on collector ring segments cut for a predetermined arc. The brushes carry electric current for the lamp and motor. A resistance is connected in series with the motor when the motor is to be slowed down during portion of a revolution. Having a reflector or lens rotate about a stationary lamp is also mentioned.
In U.S. Pat. No. 4,104,615 a rotatable prism mounted with a nonrotatable source of light causes the resulting light beam to revolve.
U.S. Pat. No. 4,153,926 shows one lighting apparatus that rotates and another one that is mechanically oscillated.
U.S. Pat. No. 2,928,072 shows a rotary mirror arrangement, a stationary light source and an electric motor. The rotary mirror rotates and oscillates at the same time.
U.S. Pat. No. 3,133,263 describes a direction indicator utilizing two rotating lights producing different flash patterns when viewed from different positions.
U.S. Pat. Nos. 2,409,046 and 2,417,934 show white and red train lights which can be rotated into and out of viewing position. A limit switch halts the rotation. The selected white or red lamp which is made to be in register in the viewing position is caused to oscillate by a motor and mechanical linkage.